Infrared electronic thermometer and method for measuring temperature

ABSTRACT

An electronic infrared thermometer is disclosed comprising a housing forming an interior chamber, a pyroelectric sensor mounted within the chamber for sensing temperature change and generating an indicative electrical signal, means for directing infrared radiation from the object to be measured to the pyroelectric sensor, a shutter assembly for controlling the passing of infrared radiation to the pyroelectric sensor, an ambient temperature sensor for sensing ambient temperature within the interior chamber and generating an electrical signal indicative thereof, an electrical circuit for processing the electrical signals to calculate the temperature of the object to be measured, and an indicator for indicating the calculated temperature. The process for measuring the temperature of an object is also disclosed comprising shielding the pyroelectric sensor from infrared radiation from exterior to the thermometer housing, selectively exposing the pyroelectric sensor to infrared radiation substantially solely from the object to be measured to generate a first electrical signal related to the absolute temperature of the object to be measured, sensing the ambient temperature of the pyroelectric sensor and generating a second electrical signal proportional thereto, and electrically processing the first and second electrical signals to calculate the temperature of the object to be measured.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 724,339, filedApr. 17, 1985, now abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to an electronic thermometer and moreparticularly to a noncontacting infrared electronic thermometer andmethod for measuring the temperature of an object.

The temperature of an object, such as the human body, can be determinedby using a contact thermosensor or by measuring the naturally radiatedenergy from the body such as the radiated energy in the far infraredrange. The infrared radiation is directly related to temperature of theobject and can be utilized to determine the temperature of the body.

It is an object of the present invention to provide a new and improvednoncontacting electronic thermometer which is accurate, reliable andeconomical to manufacture.

Another object of the invention is to provide a noncontacting electronicthermometer for measuring the temperature of an object virtuallyinstantaneously.

A further object of the invention is to provide a noncontactingelectronic thermometer for medical use which is compact, inexpensive andconvenient and easy to use.

A further object of the invention is to provide a heat detector formedical use which detects warm spots on the surface of the skin.

A still further object of the invention is to provide a method formeasuring the temperature of a body utilizing a high-speed pyroelectricinfrared sensor and a relatively slow speed ambient temperature sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical broken away perspective view of theelectronic thermometer of the present invention.

FIG. 2 is a diagrammatical schematic view of the electronic thermometerof the present invention.

FIG. 3 is a diagrammatical longitudinal sectional view of thepyroelectic sensor.

FIG. 4 is a diagrammatical sectional view of the pyroelectric filmmaterial of the pyroelectric sensor of FIG. 3.

FIG. 5 is a diagrammatical longitudinal sectional view of anotherembodiment of a pyroelectric sensor.

FIG. 6 is a diagrammatical sectional view of the beam aiming element ofFIG. 2.

FIG. 7 is an electrical schematic diagram of the amplifier circuit ofFIG. 2.

FIG. 8 is a real time graphical representation of the operational sensorsignal.

FIG. 9 is a diagrammatical schematic view of a calibration assembly forthe electronic thermometer.

FIG. 10 is a graphic view of the wave forms produced in the calibrationassembly of FIG. 9.

FIG. 11 is another embodiment of the electrode configuration of thepyroelectric sensor of FIG. 9.

FIG. 12 is a further embodiment of the electrode configuration of thepyroelectric sensor of FIG. 9.

FIG. 13 is a diagrammatical schematic view of an alternate calibrationassembly.

FIG. 14 is a diagrammatical perspective view of a heat detector.

FIG. 15 is a diagrammatical schematic view of the heat detector of FIG.14.

FIG. 16 is a diagrammatical longitudinal sectional view of an additionalembodiment of a pyroelectric sensor.

FIG. 17 is a diagrammatical longitudinal sectional view of a furtherembodiment of a pyroelectric sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings wherein like numerals are used to identify thesame or like parts, the electronic thermometer of the present inventionis generally designated by the numeral 10. Referring to FIGS. 1 and 2,thermometer 10 generally comprises a housing 12 forming an interiorchamber 13, a barrel or wave guide 14 for directing infrared radiationinto the chamber 13, a shutter assembly 16 for controlling the passageof infrared radiation through the barrel 14, a pyroelectric sensorassembly 18, an ambient temperature sensor 20, and an electronic circuit22.

The housing 12 has an elongated lower end 24 which forms a pistol griptype handle of convenient size for one hand operation The upper end 26of the housing 12 forms the interior chamber 13 for mounting thepyroelectric sensor assembly 18 and the ambient temperature sensor 20,and provides a shield to exterior infrared radiation other than thatreceived through the barrel 14.

The barrel 14 is mounted to the forward side 28 of housing 12 inalignment with the pyroelectic sensor 18 so as to direct or aim infraredradiation from the object 11 to be measured to the pyroelectric sensormounted within the chamber 13. The barrel 14 is preferably made of metaland is interconnected to the pyroelectric sensor 18 so as to be inthermal equilibrium therewith. Alternately, the interior of the barrelmay be metallized.

Referring to FIG. 6, the barrel 14 is cylindrically shaped with asmooth, shiny interior surface 30 to facilitate transmission of infraredradiation from the open receiving end 32 to the pyroelectric sensor 18and to provide a low emissivity to reduce error generated by secondaryradiation from the barrel 14 in the event the barrel temperature differssomewhat from the temperature of the pyroelectric sensor 18. The overalllength of barrel 14 determines the angle of view A as shown in FIG. 6and for most medical applications, the length of the barrel ispreferably in the range of 2-10 centimeters.

Preferably, the outer surface 34 of the barrel 14 is thermally isolatedfrom ambient heat sources such as the human body by a protectivethermoisolator coating 36. An acceptable thermoisolator coating isplastic, e.g., a plastic made from a phenolic resin. The exteriorsurface of the protective coating 36 is shiny to reflect outside heat.As shown in phantom line in FIG. 6, a removable disposable protectivecover 38 may be utilized in certain applications to prevent the barrelsurface from contacting the object to be measured, e.g., to preventcontamination. The cover 38 has a low thermoconductivity and anacceptable material is a polyethylene type material. Alternately, asuitable optical assembly such as one comprising a polyethylene Fresnellens may be utilized in place of the barrel 14 to direct the infraredradiation from the object 11 to the pyroelectric sensor 18.

The pyroelectric sensor assembly 18 is mounted within the chamber 13and, as shown in FIG. 2, is positioned in alignment with the barrel 14so as to receive the infrared radiation passing through the barrel 14.Referring to FIG. 3, the pyroelectric sensor assembly 18 comprises abase 40 forming an open-ended interior recess 42 for mounting apyroelectric film 44 to receive the infrared radiation from the barrel14. The pyroelectric film 44 is clamped between an outwardly disposedperipheral clamp 46 and an inwardly disposed peripheral contact ring 48.The contact ring 48 is securely mounted within the recess 42 in spaceddisposition to the base 40. An insulating insert spacer 50 electricallyinsulates the contact ring 48 from the base 40 and, as shown in FIG. 3,the insert 50 cooperatively engages the interior end of the contact ring48 so as to maintain the contact ring in spaced disposition relative tothe base 40.

In the illustrated embodiment, the pyroelectric film is an ultra thinfoil of pyroelectric material such as polyvinylidene fluoride (PVDF). Ifelectrically polarized, such a film exhibits a pyroelectric effect inthat it is able to generate an electrical charge in response to a changeof its temperature produced by the receipt of infrared radiation. Otherconfigurations and materials such as those generally disclosed in Smithet al, U.S. Pat. No. 4,379,971 and Cohen et al, U.S. Pat. No. 3,809,920(which disclosures are incorporated herein by reference) may also beutilized. In the illustrated embodiment, polyvinylidene fluoride is apreferable material since it is sensitive to minute and rapidtemperature changes in response to the infrared radiation utilizedherein and is relatively economical.

Referring to FIG. 4, the pyroelectric film 44 may be of varyingthicknesses ranging from 5 to 100 microns with the thickness beingdetermined by the sensitivity and speed response desired for aparticular application. A pair of planar electrodes 52, 54 are fixed onopposite sides of the polyelectric film 44 with the electrode 52 facingoutwardly from the recess 42 to first receive the infrared radiationfrom the barrel 14. In the illustrated embodiment, the outer electrode52 is black to provide high emissivity and absorption of infraredradiation and the inner electrode 54 is nontransparent and highlyreflective of infrared radiation. Alternately, the outer electrode 52may be transparent to far infrared radiation and the inner electrode 54may be reflective to provide a greater speed response and sensitivity.

In assembly, the base 40 and the clamp 46 are electrically connected toprovide shielding for the pyroelectric film 44. The base 40 and theouter electrode 52 are connected to ground by the ground lead 56. Theinner electrode 54 is electrically connected to the lead wire 58 throughthe contact ring 48. The lead wires 56, 58 connect the pyroelectricsensor assembly 18 to the electronic circuit 22. The pyroelectric film44 is polarized during the manufacturing process so that the polarity ofthe signal generated in response to the reception of infrared raditionis compatible with the electronic circuitry being utilized. In theillustrated embodiment, the pyroelectrc film is appropriately polarizedso that the inner kelectrode generates a negative signal in response toa positive temperature change. In operation, the pyroelectric sensor 18senses temperature change and generates an electrical signal indicativethereof.

In practice, it has been found that pyroelectric sensor assemblies 18employing pre-polarized pyroelectric films 44 are substantial superiorin terms of cost and ease of manufacture to prior art infrared sensorsemploying, for example, charged polymer films, thermocouples,thermopiles, or the like. Specifically, in comparison to the prior artsensors, film 44 has a relatively large area, e.g., on the order of 1cm², and is sensitive to infrared radiation impinging on essentially anypart of that area. Accordingly, the infrared thermometers of the presentinvention do not require systems for focusing infrared radiation on thesensor, such as, focusing tubes, parabolic mirrors, lenses, or the like.This makes for a significantly simpler device, which in turn, lowers theoverall cost of the device and makes the device easier to manufacture.

The ambient temperature sensor 20 is mounted within the interior chamber13 in thermal equilibrium with the pyroelectic sensor 18, the barrel 14,and the shutter element 66 so as to sense or monitor the internaltemperature of the housing 12. The ambient temperature sensor 20 sensesthe internal temperature of the housing 12 and generates an electricalsignal proportional thereto which is applied to the electronic circuit22 through the connector 64. Acceptable temperature transducers that maybe utilized for such ambient temperature sensing include thermistors,thermopiles, semiconductors, etc. Importantly, the ambient temperaturesensor may be relatively slow-acting as contrasted to the fast-actingpyroelectric sensor and need only have a response time sufficient totrack the changes of the internal ambient temperature of the chamber 13.

The exposure of the pyroelectric film 44 to infrared radiation directedthrough the barrel 14 is controlled by the shutter assembly 16. Theshutter assembly 16 comprises a shutter 66, a shutter control mechanism68, and a manually actuated pushbutton 70. The shutter 66 isoperationally mounted at the inner end 33 of the barrel 14 so as to beactuable between a normally closed position closing off the transmissionof infrared energy from the barrel 14 to the pyroelectric sensor 18 andan open position permitting infrared energy to pass from the barrel 14to the pyroelectric sensor 18.

The shutter control mechanism 68 is of conventional design providing ahigh shutter opening speed in the range of 5-25 milliseconds. Acceptableconventional mechanisms include a mechanical trigger assembly, asolenoid actuated means, a stepper motor assembly, etc. The shutter 66is actuated to an open position by depression of the pushbutton 70 andremains in the open position a sufficient time to permit thepyroelectric sensor 18 to generate the electrical signal responsive toshutter opening as explained hereinafter. The shutter 66 is returned toits normally closed position after approximately 200 milliseconds. Amechanical timing gear is utilized to control the duration of theshutter 66 in the open position. Alternately, the timing gear may beelectro-mechanical.

The shutter control mechanism 68 includes noise supression elements andshock absorbers to reduce acoustical noise and other mechanical forcesduring the shutter opening operation to control the accuracy of theresponsive electrical signal generated by the pyroelectric sensor 18.Since the pyroelectric film 44 has piezoelectric properties, excessiveacoustical noise or mechanical force can produce detrimental error andnoise in the electrical signal generated by the pyroelectric film 44 inresponse to temperature changes.

The shutter 66 is configured to have a low thermal conductivity from itsouter surface 72 to its inner surface 74 in order to prevent the shutterfrom becoming an extrinsically dependent secondary source of radiationto the pyroelectric film 44. Both the inner and outer surfaces ofshutter 66 are reflective in nature in order to reduce emissivity andheating from external sorces. The shutter 66 is also mounted within thechamber 13 so as to be in thermal equilibrium with the pyroelectricsensor 18.

The electronic circuit 22 includes an amplifier circuit 60, amicroprocessor or microcontroller 76, a shutter sensor switch 77 and adigital visual display device 78. The microprocessor 76 isinterconnected to the ambient temperature sensor 20, the amplifiercircuit 60 and the shutter sensor switch 77 to receive electrical inputsignals indicative of the internal ambient temperature of thethermometer housing 12, the actuation of shutter assembly 16, and thetemperature differential between the pyroelectric sensor 18 and theobject to be measured. The microprocessor 76 is of conventional designhaving suitable data and program memory and being programmed to processthe electrical signal from the ambient temperature sensor 20 and theamplified electrical signal from the pyroelectric sensor 18 inaccordance with the following description to calculate the absolutetemperature of the body 11 to be measured. Based upon the calculatedtemperature of the subject 11, the microprocessor 76 generates a controlsignal to drive the display device 78 to visually indicate thecalculated temperature.

More specifically, the amplitude of the electrical signal generated bythe pyroelectric sensor is a nonlinear function of the differencebetween the temperature of the subject to be measured and thetemperature of the sensor prior to exposure to the radiation emitted bythe subject, i.e., the difference between the temperature of the subjectand the ambient temperature of the thermometer. The generalcharacteristics of this function can be described in terms of theStefan-Boltzman equation for radiation and the Fourier equation for heattransfer. Both these equations, however, are highly non-linear.Moreover, there exists no known analytical relationship between theamount of radiation striking a pyroelectric film, such as a PVDF film,and the voltage produced by the film.

In accordance with the present invention, it has now been found thatnotwithstanding these non-linearities and the lack of an analyticalrelationship for film output, the temperature of a subject can beaccurately determined using pyroelectric films by means of the followingprocedure. First, the voltage V_(ir) produced by the film in response toradiation from the subject is approximated by the formula:

    V.sub.ir =f(T.sub.a)(T.sub.s.sup.4 -T.sub.a.sup.4)         (1)

where T_(s) is the absolute temperature of the subject, T_(a) is theabsolute ambient temperature determined from ambient temperature sensor20, and f(T_(a)) is a polynomial in T_(a), namely,

    f(T.sub.a)=a.sub.0 +a.sub.1 T.sub.a +a.sub.2 T.sub.a.sup.2 +a.sub.3 T.sub.a.sup.3 +. . .

Next, the coefficients a₀, a₁, a₂, a₃, etc. are determined for theparticular sensor design and type of film being used by measuring V_(ir)for a series of known T_(s) 's and T_(a) 's, substituting those valuesinto equation 1, and solving the resulting set of simultaneous equationsfor the polynomial coefficients. In practice, it has been found that formeasuring body temperatures, sufficient accuracy can be achieved throughthe use of only three terms, i.e., through the use of a second orderpolynomial in T_(a). For other applications, where greater accuracy maybe required, more terms can be used if desired.

Finally, the temperature of a subject whose temperature is to bemeasured is determined by microprocessor 76 by evaluating the followingequation using V_(ir) from pyroelectric sensor 18, T_(a) as derived fromambient sensor 20, and the polynomial coefficients a₀, a₁, a₂, a₃, etc.determined as described above:

    T.sub.s =(V.sub.ir /f(T.sub.a)+T.sub.a.sup.4).sup.1/4

The microprocessor 76 is thus adapted to provide the necessary analysisof the electrical signals from the ambient temperature sensor and thepyroelectric sensor, including appropriate scaling, correction, etc., tocalculate absolute temperature. The calculated temperature is processedinto a digital format for storage in memory and for generating a controlsignal to drive the digital display. In practice, using the aboveprocedure and a PVDF film, it has been found that body temperature canbe reliable measured with the thermometer of the present invention towithin approximatelu 0.1° C.

Referring to FIG. 8, a graphic representation of V_(ir) is shown for anexemplary temperature measurement of an object having a temperaturegreater than the internal ambient temperature of the thermometer. Asindicated,the pyroelectric sensor signal (V_(ir)) quickly reaches itsmaximum or peak value after the opening of the shutter and starts toslowly decay. The rate of decay of the signal is dependent upon variousphysical parameters of the pyroelectric film 44 such as thickness,emissivityl, thermal time constant, etc. In the illustrated embodiment,the microprocessor 76 is responsive only to the peak absolute value ofthe pyroelectric sensor signal so that the actual period the shutterremains open is not critical as long as the shutter is open long enoughto allow the signal to reach its peak absolute value. Where the subjectbeing measured has a temperature greater than the ambient temperature ofthe thermometer, the peak absolute value of the voltage signal is amaximum voltage as shown in FIG. 8, whereas the peak absolute valuewould be a minimum voltage if the subject had a temperature lower thanthe ambient temperature of the thermometer. After the microprocessor 76determines the peak value, the measurement is complete and themicroprocessor becomes insensitive or nonresponsive to further inputsignals from the pyroelectric sensor.

Alternatively, the microprocessor 76 may be programmed to calculate theabsolute temperature of the subject by integration of V_(ir) over apredetermined fixed time frame t₀ according to the following equation:##EQU1## where, k_(i) =a calibration factor in 1sec.

The integration method of measurement calculation is more resistantagainst high frequency noise such as may be picked up by thepyroelectric sensor and is particularly advantageous where thetemperature of the subject to be measured is relatively close to theinternal temperature of the thermometer.

It is important to note that for both the peak absolute value approachand the integration approach, the signal being measured is the transientresponse of the pyroelectric film to the infrared radiation reaching thefilm during the time when shutter 66 is open, that is, in accordancewith the present invention, the transient response of the film to asingle pulse of infrared radiation is all that is measured. This is indirect contrast to prior art infrared thermometers which either measuredthe steady state response of the sensor or employed a chopper to breakup the incoming infrared radiation into a series of pulses and thenaveraged the response of the sensor to those pulses. By measuring thetransient response, the thermometer of the present invention has afaster response time than prior art thermometers which had to wait untila steady state was achieved; by using only one pulse, the presentinvention avoids the need for both a chopper and averaging circuitry,thus allowing for the production of a less complicated and lessexpensive device which is easier to manufacture. Moreover,notwithstanding the fact that only one pulse of infrared radiation ismeasured, the thermometer of the present invention has been surprisinglyfound to consistently and accurately measure body temperatures.

Referring to FIG. 7, the amplifier circuit 60 of the present inventionis shown in detail. In the illustrated embodiment, the pyroelectricsensor 18 generates a negative signal in response to positivetemperature change. The pyroelectric sensor signal is applied via lead58 to the negative input terminal of the amplifier 61 and an internallygenerated reference voltage (V_(ref)) is applied to the positive inputterminal. Preferably, the amplifier has a JFET or CMOS input stage andis a current-to-voltage converter whose input impedance is dependentupon the bias resistor 80 and the ratio of resistors 82, 84. Capacitor86 provides negative feedback to maintain the stability of the amplifierand reduce high-frequency noise. Capacitor 88 blocks out low frequencydrifts and offset voltages in the voltage output signal V_(out) which isapplied to the input of microprocessor 76 by lead 87. The analog switch90 is normally in a closed position prior to actuation of the shutterassembly 16 so that the ampifier output voltage is equal to theinternally generated reference voltage. The analog switch 90 isconnected by lead 92 to the shutter actuation sensor switch 77 whichgenerates an indicator signal upon actuation of the shutter assembly 16by the pushbutton 70. Upon actuation of the shutter assembly, theindicator signal generated by the sensor switch 77 causes the analogswitch 90 to open and the voltage output V_(out) is then the amplifiedsignal V_(ir) from the pyroelectric sensor 18 which changes rapidly inresponse to the infrared radiation from the subject to be measured.

In operation, the outer end of the barrel 14 is positioned in spaceddisposition adjacent the subject 11 to be measured. Upon actuation ofthe pushbutton 70 and the opening of the shutter 66, infrared radiationfrom the subject 11 is directed along the barrel 14 to the pyroelectricfilm 44 of the pyroelectric sensor 18. The pyroelectric film 44generates an electrical signal which is a function of the change intemperature caused by the infrared radiation from the subject 11. Basedupon the ambient temperature of the interior of the thermometer assensed by the ambient sensor 20 and the temperature change of thepyroelectric sensor assembly caused by the infrared radiation reachingthe sensor from the subject, the temperature of the subject iscalculated by the microprocessor 76 and displayed on the digital display78. The response time of the thermometer is relatively fast being in theorder of 0.25 seconds. As can be seen from the foregoing, a fasttemperature reading is obtained with a noncontacting electronicthermometer which is easy to use and economical to manufacture.

Another embodiment of a pyroelectric sensor assembly is shown in FIG. 5being generally designated by the numeral 19. The pyroelectric sensor 19comprises a contact ring or insert 48 integrally formed with a contactpin 58 which extends through the insulating insert 50. The pyroelectricfilm 44 is clamped between the contact ring 48 and the clamp 46 with theclamp 46 being held in place by the rolled edges 41 of the base 40. Theouter electrode 52 is connected to ground through the clamp 46 and thebase 40 while the inner electrode 54 is connectable to the amplifiercircuit 22 through the contact ring 48 and the contact pin 58. Theremaining elements function similarly to the embodiment of FIG. 3 andneed not be described in detail. The configuration of FIG. 5 isparticularly suited for economical high-volume manufacture and alsofacilitates the assembly of the thermometer 10 because of itscompatibility with automated manufacturing processes.

Additional embodiments of the pyroelectric sensor assembly are shown inFIGS. 16-17. In FIG. 16, polymer film 44, having electrodes 52 and 54 onits front and rear faces, is mounted inside nonconductive housing orsupport 150. The film can be mounted to the housing in various ways,such as, through the use of glue, heat welding, or the like. To protectthe film, the front face of the sensor can include a cover 163 made ofmaterial which is transparent to far infra-red radiation, such as,polyethylene. To equalize the pressure on both sides of the film,housing 150 preferably includes an opening 160 in its rear wall leadinginto the cavity formed by the film and the walls of the housing.

Two contacts 161 and 162 are molded into housing 150. Contact 162 isconnected to front electrode 52, and contact 161 is connected to rearelectrode 54. These connections can be made by physical contact or via aconductive media, such as, a conductive epoxy, e.g., Rgon.

FIG. 17 shows a modified version of the sensor assembly of FIG. 16wherein ambient sensor 20 is mounted in the same housing 164 as polymerfilm 44. In particular, ambient sensor 20 is mounted in the cavityformed by film 44 and the walls of housing 164. In this way, betterthermal coupling between the film and the ambient temperature sensor isachieved.

Referring to FIG. 9, an optional calibration circuit 94 is shown forcalibrating the pyroelectric sensor signal to compensate for possiblevariations due to material aging, temperature drifts, instability ofelectronic components, etc. which may produce unacceptable error in thetemperature measurement. The pyroelectric film 44 has piezoelectricproperties which are necessarily subjected to the same environmentalfactors (such as material aging, temperature, etc.) as its pyroelectricproperties. Consequently, calibration may be attained by an electricalcalibration, i.e., piezo-calibration, as opposed to a thermalcalibration, i.e, pyro-calibration. The application of a predeterminedreference signal to the piezoelectric-pyroelectric film will generate amechanical stress or deflection at one portion of the film and thatstress may be sensed in the other portion of the film since it generatesa responsive signal. Thus, calibration is attained through applicationof a predetermined electrical calibration signal to the pyroelectricfilm prior to each temperature measurement calculation to generate aresponsive signal. The responsive signal is utilized by the microprocessor as a correction factor in the temperature calculations.

Referring to FIG. 9, the outer planar electrode 96 on the outwardlyfacing surface of the pyroelectric film 44 is comprised of two separatespaced electrode segments 98, 100. The electrode segment 100 isconnected to amplifier circuit 60. The electrode segment 98 is connectedto switch 102 which alternately interconnects the electrode segment 98to either the amplifier circuit 60 or to an excitation signal circuit104.

The excitation circuit 104 is of conventional design for producing apredetermined electrical calibration signal 106 adapted to excite thepiezoelectric film to produce a mechanical stress and, in turn, aresponsive electrical signal 108 (FIG. 10). The value of the responsiveelectrical signal at the time of assembly and initial calibration of thethermometer 10 will constitute a predetermined standard and is stored inmemory. The switch 102 and the excitation signal circuit 104 arecontrolled by the microprocessor 76 and, upon command from themicroprocessor 76 during the calibration operation, the excitationsignal circuit generates a predetermined electrical calibration signal106.

The calibration operation is performed with the shutter 66 in a closedposition as diagrammatically shown in FIG. 9. Prior to opening theshutter 66, the switch 102 interconnects the electrode segment 98 to thesignal excitation circuit 104 and the predetermined electrical signal106 is applied to the electrode 98. Due to the piezoelectric propertiesof the pyroelectric film 44, this causes a mechanical stress and, inturn, the mechanical stress causes the piezoelectric film 44 to generatea responsive electrical signal 108 in electrode 96 which is conducted tothe amplifier circuit 60 via the electrode segment 100. Since themechanical stress calibration signal is a predetermined value, deviationin the response signal 108 is indicative of changes in the pyroelectricsensor 18 and the degree of deviation from the predetermined standardprovides the necessary calibration information for appropriatecorrection by the microprocessor 76. Immediately following thecalibration operation, the switch 102 interconnects the electrodesegment 98 to the amplifier circuit 60 which thereby doubles theinfrared sensitivity area of the film and the temperature measurementoperation is performed as previously described relative to theembodiment of FIGS. 1 and 2.

Preferably, calibration is performed immediately prior to eachmeasurement operation to ensure reliable and accurate absolutetemperature measurement. Any changes in the pyroelectric properties ofthe pyroelectric film 44 due to aging, environment, etc. will beautomatically compensated for by the microprocessor 76 in calculatingthe absolute temperature of the subject.

Referring to FIGS. 11 and 12, alternate embodiments of the planarelectrode segments 98, 100 are shown. In FIG. 11, the electrode segments98, 100 are interdigitized on the inward facing surface of thepyroelectric film 44. In FIG. 12, the electrode segment 98 is coaxial tothe electrode segment 100 and the electrode segment 98 may bepermanently connected to the excitation network 104 thereby eliminatingthe necessity for switch 102. However, the thermal sensitive area of thepyroelectric film 44 will be limited to the electrode segment 100.

Referring to FIG. 13, an alternate configuration for calibrating thepyroelectric sensor assembly 18 is shown. In this configuration, aheating element 108 is controlled by a controller 110 to provide apredetermined stable infrared radiation level upon command from themicroprocessor 76.

The inner surface of the shutter 66 has a reflective plate 114 alignedwith the heating element 108 and the pyroelectric sensor 18 so as toreflect the infrared beam 112 from the heating element 108 to thepyroelectric sensor assembly. Necessarily, the generated infraredradiation beam 112 is stable under operating conditions. The electricalsignal generated by the pyroelectric sensor in response to the infraredbeam 112 provides a reference signal to the microprocessor 76 to enableit to calculate the amount of correction required in the subsequenttemperature measurement calculation. Again, the calibration operation isperformed with the shutter 66 in a closed position and preferably thecalibration operation is performed prior to each temperature measurementoperation.

Alternately, the microprocessor 76 may be provided with a predeterminedtable of error correction data based upon the known sources of error andchanges in the responsive characteristics of the pyroelectric film. Themicroprocessor is programmed to adjust the calculated absolutetemperature in accordance with the error correction data.

As can be seen, a new and improved noncontacting electronic thermometerhas been provided which is accurate, reliable, and economical tomanufacture. In operation, the electronic thermometer is compact andeasy to use and measures absolute temperature of an object virtuallyinstantaneously.

Referring to FIGS. 14 and 15, a further embodiment of the presentinvention is shown in the nature of a heat differential detector 130 forthe detection of warm spots on a surface. The detection of warm spots isoften desirable to locate bone fractures, tissue inflammation, etc. Theheat detector 130 generally comprises a housing 121, a barrel 14, apyroelectric sensor assembly 18 having a pyroelectric film 44, anelectric circuit 22 and an indicator light 116.

The barrel 14 and pyroelectric sensor 18 function as previouslydescribed with respect to the embodiment of FIG. 1. The electroniccircuit 22 generally comprises an amplifier 60, a comparator 118, and anindicator circuit 120. The output of the amplifier 60 is connectedthrough capacitor 122 to the comparator 118. The threshold point of thecomparator may be varied by the potentiometer 124. A pushbutton resetswitch 126 permits discharge of the capacitor 122 to ground. Theindicator circuit 120 is connected to the comparator 118 and drives theindicator light 116 or any other acceptable indicator such as an audiotone generator, etc.

In operation, the capacitor 122 is discharged by momentary actuation ofthe switch 126 prior to beginning the sensing operation. To sense ordetect a warm spot, as for example the warm spot 128 on skin surface 131as shown in FIG. 14, the heat detector 130 is positioned so that theopen receiving end 32 of the barrel 14 is adjacent the surface 131. Theheat detector 130 is then moved along the surface at approximately aconstant rate of speed. When the warm spot 128 enters the field of viewof the barrel 14, the increase in infrared radiation from the warm spot128 causes the pyroelectric sensor 18 to generate an indicativeelectrical signal. The amplified electrical signal is applied to thecomparator 118 and if the electrical signal exceeds the set thresholdvalue of the comparator, the indicator circuit 120 will be actuated todrive the indicator light 116. The threshold point of the comparator mybe varied depending on the particular heat sensing application.

Accordingly, a heat detector is provided which is convenient and easy touse and which is economical to manufacture.

As will be apparent to persons skilled in the art, various modificationsand adaptions of the structure above-described will become readilyapparent without departure from the spirit and scope of the invention,the scope of which is defined in the appended claims.

What is claimed is:
 1. A thermometer comprising:a housing; a sensorcarried by said housing and responsive to infrared radiation forgenerating an electrical signal which exhibits a transient response uponinitial receipt of said radiation; means, carried by said housing, inoptical alignment with said sensor, for directing infrared radiationfrom an object, the actual temperature of which is to be measured, toimpinge upon said sensor; means, carried by said housing, for enablingresponse of said sensor to said radiation; and electrical means carriedby said housing and responsive essentially only to said transientresponse of said signal for processing said signal to develop anindication of the actual temperature of said object.
 2. A thermometer asdefined in claim 1 in which said directing means is so interconnected tosaid sensor as to be in thermal equilibrium therewith.
 3. A thermometeras defined in claim 1 in which said directing means is in itself of lowemissivity to infrared radiation in avoidance of contributing toradiation directed from said object to said sensor.
 4. A thermometer asdefined in claim 1 in which said directing means exhibits substantialthermal isolation from ambient sources of heat external to saiddirecting means.
 5. A thermometer as defined in claim 1 in which saidsensor includes a pyroelectric material which generates an electricalcharge in response to a change in its temperature produced by itsreceipt of said radiation.
 6. A thermometer as defined in claim 1 inwhich said sensor is a pyroelectric element sandwiched between a firstelectrode disposed in use to face said object and a second electrode onthe opposed surface of said element, said first electrode exhibiting thecharacteristic of high emissivity and absorption of said infraredradiation.
 7. A thermometer as defined in claim 1 in which said sensoris a pyroelectric element sandwiched between a first electrode disposedin use to face said object and a second electrode on the opposed surfaceof said element, and in which said second electrode is nontransparent toand highly reflective of said infrared radiation.
 8. A thermometer asdefined in claim 1 in which said sensor is a pyroelectric elementsandwiched between a first electrode disposed in use to face said objectand a second electrode on the opposed surface of said element, and inwhich said first electrode is transparent to far infrared radiation andsaid second electrode is substantially reflective thereto.
 9. Athermometer as defined in claim 1 in which said directing means deliverssaid infrared radiation from said object spread over an area relativelylarge laterally to the direction of the impingement of said radiationupon said sensor, and in which said sensor correspondingly responds overan area encompassing said spread.
 10. A thermometer as defined in claim1 in which said electrical means automatically becomes insensitive tofurther input signals from said sensor after receipt of said transientresponse.
 11. A thermometer as defined in claim 1 in which saidelectrical means includes means for calculating the absolute temperatureof said object by integration of the level of said response over a fixedtime frame.
 12. A thermometer as defined in claim 1 in which said sensorexhibits said transient in response to a single pulse of said radiation,and in which said electrical means responds only to said single pulse.13. A thermometer as defined in claim 1 which said sensor is mountedwithin said housing, and in which said housing includes means toequalize the pressure on both sides of said sensor.
 14. A thermometer asdefined in claim 1 in which a heating element is carried by said housingin a position to yield heat to said sensor and provide a calibratingstable infrared level imposed upon said sensor;and in which saidelectrical means responds to said sensor as heated by said element. 15.A thermometer as defined in claim 1 in which said electrical meansincludes an electronic memory which contains a predetermined table ofcorrection data in accordance with known possible sources of error andchanges in responsive characteristics of said sensor, with saidelectrical means programmed to adjust the calculated absolutetemperature of said object in accordance with said correction data. 16.The thermometer of claim 1 wherein said directing means comprises anelongated guide of predetermined length having an outer end to receiveinfrared radiation from the object to be measured and an inner end inoperative alignment with said sensor, in which said guide is mounted tosaid housing and interconnected to said sensor so as to be in thermalequilibrium therewith and with said guide having a smooth and shinyinterior surface and an outer surface, and means on said outer surfacefor thermally isolating said outer surface from external ambient heatsources.
 17. The thermometer of claim 16 wherein said means forthermally isolating comprises a thermoisolator coating on said outersurface.
 18. A thermometer as defined in claim 1 in which said sensor isresponsive to a predetermined electrical calibration signal;in whichsaid electrical means include means for applying to said sensor saidelectrical calibration signal; and in which said electrical meansresponds to the sensor output from said calibration signal by correctingcalculation of said actual temperature.
 19. A thermometer as defined inclaim 18 in which said electrical means at least approximately doublesthe sensitivity area to said radiation of said sensor following responseto said calibration signal.
 20. A thermometer as defined in claim 18 inwhich said sensor is a pyroelectric element sandwiched between a firstelectrode disposed to face said object and a second electrode on theopposed surface of said element, and in which one of said electrodescomprises two separate and spaced electrode segments wherein saidsegments are included in said applying means.
 21. A thermometer asdefined in claim 20 which further includes means for interconnectingsaid segments prior to said response of said sensor to said radiation.22. A thermometer as defined in claim 1 which further includes meanscarried by said housing and responsive to the ambient temperature ofsaid sensor prior to said initial receipt of said radiation forgenerating another electrical signal representative of said ambienttemperature, and in which said electrical means processes said otherelectrical signal to calculate actual temperature of said object.
 23. Athermometer as defined in claim 22 in which said housing defines aninterior chamber, and in which said ambient temperature means also isdisposed within said chamber in thermal equilibrium with said sensor.24. A thermometer as defined in claim 22 in which said ambienttemperature means exhibits its electrical signal in slow response ascompared with the response of said sensor to said radiation.
 25. Athermometer as defined in claim 22 in which said ambient temperaturemeans is mounted within a cavity defined within the interior of saidhousing.
 26. A thermometer of claim 22 wherein the temperature of theobject to be measured by said electrical means is calculated using theequation:

    T.sup.2 =(V.sub.ir /f(T.sub.a)+T.sub.a.sup.4).sup.1/4,

where T_(s) is the absolute temperature of the object to be measured,V_(ir) is the first electrical signal generated by said sensor, T_(a) isthe absolute ambient temperature determined by said electrical meansfrom said other electrical signal generated by said ambient temperaturemeans, and f(T_(a)) is a polynomial in T_(a) given by equation:

    f(T.sub.a)=a.sub.0 +a.sub.1 T.sub.a +a.sub.2 T.sub.a.sup.2 +a.sub.3 T.sub.a.sup.3 +. . . ,

where the polynomial coefficients a₀, a₁, a₂, a₃ . . . are determined byexposing said sensor at a known ambient temperature to objects havingknown temperatures.
 27. The thermometer of claim 26 wherein the thesignal V_(ir) is approximated by using the formula:

    V.sub.ir =f(T.sub.a) (T.sub.s.sup.4 -T.sub.a.sup.4).


28. A thermometer as defined in claim 1 in which said enabling meansfurther includes:a shutter carried by said housing and movable between afirst position blocking transmission of said radiation from saiddirecting means to said sensor and a second position which enablespassage of said radiation to said sensor; means for moving said shutterbetween said first and second positions; and means for controllingmovement of said shutter to enable response of said sensor to saidradiation to exhibit said transient response upon receipt of saidradiation.
 29. A thermometer as defined in claim 28 in which saidcontrolling means enables movement of said shutter to said firstposition substantially upon termination of said transient response. 30.A thermometer as defined in claim 28 in which said controlling meansincludes means for suppressing and absorbing noise and shock developedupon the movement of said shutter between said first and secondpositions.
 31. A thermometer as defined in claim 28 in which saidhousing includes an interior chamber in which said sensor is contained,and in which said shutter is mounted as to be in thermal equilibriumwith said sensor.
 32. A thermometer as defined in claim 28 whichincludes means for supplying said electrical means with input signalsindicative of the ambient temperature of the said sensor, and in whichthe actuation of said shutter enables the calculation of the temperaturedifferential between said sensor and said object.
 33. A thermometer asdefined in claim 28 in which said electrical means includes means forresponding to actuation of said shutter in order to provide anindication signal that causes said transient response to be measured.34. A thermometer as defined in claim 28 in which said shutter exhibitsa low thermal conductivity between a first surface which faces saiddirecting means and a second surface which faces said sensor.
 35. Athermometer as defined in claim 28 in which both of said surfaces ofsaid shutter are reflective to the said radiation.
 36. A method formeasuring the temperature of an object with a thermometer having ahousing providing an interior chamber and an ambient temperature sensorand a pyroelectric infrared sensor mounted within the chamber comprisingthe steps of:shielding said pyroelectric sensor from infrared radiationfrom exterior to the said thermometer housing; selectively exposing saidpyroelectric sensor to infrared radiation substantially solely from theobject to be measured to generate a first electrical signal which is afunction of the temperature of the object to be measured and the ambienttemperature of said pyroelectric sensor immediately prior to saidselective exposing; sensing the ambient temperature of said pyroelectricsensor and generating a second electrical signal proportional thereto;and electrically processing said first and second electrical signals tocalculate the temperature of the object to be measured.
 37. The methodof claim 1 wherein the temperature of the object to be measured iscalculated using the equation:

    T.sub.s =(V.sub.ir /f(T.sub.a)+T.sub.a.sup.4).sup.1/4,

where T_(s) is the absolute temperature of the object to be measured,V_(ir) is the first electrical signal generated by said pyroelectricsensor, T_(a) is the absolute ambient temperature determined from saidsecond electrical signal, and f(T_(a)) is a polynomial in T_(a) given bythe equation:

    f(T.sub.a)=a.sub.0 +a.sub.1 T.sub.a +a.sub.2 T.sub.a.sup.2 +a.sub.3 T.sub.a.sup.3 +. . . ,

where the polynomial coefficients a₀, a₁, a₂, a₃ . . . are determined byexposing said pyroelectric sensor at a known ambient temperature toobjects having known temperatures.
 38. The device method of claim 37wherein the signal V_(ir) is approximated by using the formula:

    V.sub.ir =f(T.sub.a) (T.sub.s.sup.4 -T.sub.a.sup.4).


39. The method of claim 36 which comprises calibrating the sensitivityof said pyroelectric sensor prior to selectively exposing saidpyroelectric sensor to infrared radiation from the object to bemeasured.
 40. The method of claim 39 wherein the said pyroelectricsensor is adapted to exhibit piezoelectric properties and calibratingthe sensitivity of said pyroelectric sensor comprises:applying apredetermined calibration signal to said pyroelectric sensor so as tocause said pyroelectric sensor to generate a responsive electricalcalibration signal; and correcting said first electrical signalgenerated by said pyroelectric sensor based upon said responsiveelectrical calibration signal and a predetermined standard value. 41.The method of claim 40 wherein calibrating the sensitivity of saidpyroelectric sensor comprises:applying a predetermined level of infraredradiation to said pyroelectric sensor so as to cause said pyroelectricsensor to generate a responsive electrical calibration signal; andcorrecting said first electrical signal generated by said pyroelectricsensor based upon said responsive electrical calibration signal and apredetermined standard value.